Target Cell Access Method And Device

ABSTRACT

Embodiments of this application disclose a cell access method and a device, to provide a network slice service area identifier and network slice configuration information for a terminal device, so that the terminal device accesses a target cell. The method in the embodiments of this application includes: obtaining, by a terminal device, a network slice service area identifier from a serving access network device corresponding to a serving cell in which the terminal device is located, where the network slice service area identifier is used to indicate an area served by a network slice; determining, by the terminal device, a target cell based on network slice configuration information and the network slice service area identifier, where the network slice configuration information includes a correspondence among a network slice, an area, and a service; and accessing, by the terminal device, the target cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation U.S. patent application Ser. No.16/433,925, filed on Jun. 6, 2019, which is a continuation ofInternational Application No. PCT/CN2018/073924, filed on Jan. 24, 2018,which claims priority to Chinese Patent Application No. 201710061634.1,filed on Jan. 26, 2017. All of the afore-mentioned patent applicationsare hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the field of mobile communications, and inparticular, to a target cell access method and a device.

BACKGROUND

An increasing quantity of user cases have noticeably differentrequirements for network performance. In a fifth generation (5G) mobilecommunications system, a concept of a network slice (NS) is proposed toconstruct a related network architecture.

Currently, according to the Third Generation Partnership Project (3GPP),main types of network slices in 5G are divided into the following threetypes: an Enhanced Mobile Broadband (eMBB) service, a massive machinetype communications (mMTC) service, and an ultra-reliable and lowlatency communications (URLLC) service. The eMBB is mainly intended fora terminal with high requirements for a rate and mobility, such as amobile phone or a multimedia device. The mMTC is mainly intended for anInternet of Things device with requirements for a large scale, lowmobility, and a relatively low rate. The URLLC mainly refers to aservice or a device type with harsh requirements for a latency andreliability, such as Internet of Vehicles and security information. Forexample, a mobile phone user may access a network slice of an eMBB type,to download at high speed or watch a 4K high-definition video. A sensordevice may access a network slice of an mMTC type, to transmit a smalldata packet and update a system configuration. A user may simultaneouslyaccess one or more or all network slices, to meet a service requirementand achieve better user experience.

A procedure of selecting a network slice is divided into two steps:network slice guiding and network slice association.

Step 1 (network slice guiding): When a terminal device initiates networkconnection establishment to a selected public land mobile network(PLMN), a radio access network (RAN) forwards an establishment requestof a user to a network slice selection module of a core network (CN).The module may query information about the terminal device such assubscription information related to a network slice, a service levelagreement (SLA), load information, and a local configuration based onuseful information provided by the terminal device such as a selectedPLMN identifier, an identifier of the terminal device, and informationabout a CN capability supported by the terminal device, so as to selectan appropriate network slice for the terminal device, and allocate anappropriate NSID to the terminal device. The terminal device stores theNSID. In addition, the network slice selection module notifies the RANof configuration information corresponding to a selected network sliceentity, such as a corresponding NF identifier, so that the RANsubsequently establishes CP and UP channels between the terminal deviceand the selected network slice.

Step 2 (network slice association): After the network slice guidingends, when the terminal device re-initiates a network slice connection,for example, when the terminal device needs to initiate a servicerequest due to a service requirement, the RAN selects a corresponding NFbased on the NSID stored and reported by the terminal device and thelocally-stored configuration information of the network slice entity, soas to establish CP and UP connections between the terminal device and anetwork slice instance corresponding to the terminal device.

A current network slice guiding manner is established based on anassumption that a network can definitely select an appropriate networkslice for the terminal device. However, an actual network slicedeployment case is not considered, and some network slices may bedeployed only in a local network area. For example, a companyestablishes a network slice for employees of the company in anindustrial park, to specially serve the employees of the company.Alternatively, a network slice is deployed in a stadium, so that when auser initiates a service in the stadium, the user may enjoy a betterservice, and service experience may be improved. In this case, when theterminal device moves, a serving cell changes, and it is difficult forthe terminal device to continue enjoying a service of the network slice.Consequently, it is difficult to ensure service continuity and serviceexperience of the network slice.

SUMMARY

Embodiments of this application provide a target cell access method anda device, to provide a network slice service area identifier and networkslice configuration information for a terminal device, so that theterminal device accesses a target cell.

In view of this, a first aspect of the embodiments of the presentinvention provides a target cell access method, including:

A terminal device obtains a network slice service area identifier from aserving access network device corresponding to a serving cell in whichthe terminal device is located, where the network slice service areaidentifier is used to indicate an area served by a network slice. In theembodiments of this application, an identifier of a tracking area (TA)may be pre-allocated to each cell, for example, a TA identifier of acell 1 is TA1. Different network slices have different service ranges.For example, a network slice 1 needs to cover TA1, TA2, and TA3, anetwork slice 2 needs to cover TA2, TA4, and TA5, and a network slice 3covers only TA6. This is not limited herein. The terminal devicedetermines a target cell based on network slice configurationinformation and the network slice service area identifier, where thenetwork slice configuration information includes a correspondence amonga network slice, an area, and a service. The terminal device accessesthe target cell.

With reference to the first aspect of the present invention, in a firstimplementation of the first aspect of the present invention, the methodincludes: The terminal device obtains the network slice configurationinformation from a core network. Optionally, in some feasibleembodiments, the network slice configuration information may bepreconfigured in device storage of the terminal device or a storage unitof a subscriber identity module (SIM) card, or the configuration messagemay be sent to the terminal device by using a non-access stratum (NAS)message, and the terminal device stores the received network sliceconfiguration information.

The core network and the terminal device exchange the network sliceconfiguration information, and the serving access network device and theterminal device exchange the network slice service area identifier, sothat the terminal device senses a service range of a network slice.

With reference to the first implementation of the first aspect of thepresent invention, in a second implementation of the first aspect of thepresent invention, the method includes:

The terminal device sends a request message to the core network, wherethe request message is used to request the network slice configurationinformation. In some feasible embodiments, the terminal device mayestablish a network connection to the serving access network device, forexample, an RRC connection. After the network connection is established,the terminal device may perform uplink and downlink data communicationwith the serving access network device, and perform, by using theserving access network device, uplink and downlink data communicationwith a core network that serves the serving access network device. Theterminal device receives the network slice configuration informationfrom the core network.

The core network and the terminal device exchange the network sliceservice area identifier, so that the terminal device senses a servicerange of a network slice.

With reference to the first aspect of the present invention, in a thirdimplementation of the first aspect of the present invention, the methodincludes:

The terminal device sends an indication message to the serving accessnetwork device, where the indication message is used to indicate arequirement for a network slice. The terminal device obtains the networkslice service area identifier from the serving access network device. Inthe embodiments of this application, the terminal device may firstsynchronize with the serving access network device, for example, performdetection on a primary synchronization signal and a secondarysynchronization signal, and perform correction in time domain andfrequency domain, so as to obtain information such as a correspondingfrequency channel number and bandwidth.

When the terminal device that is using a target service moves, even ifthe serving cell changes, the terminal device can determine the targetcell based on the obtained network slice configuration information andthe obtained network slice service area identifier, and continueenjoying the target service in the target cell, so that servicecontinuity is ensured.

A second aspect of the embodiments of the present invention provides atarget cell access method, including:

A serving access network device sends a connection indication to atarget network device. The connection indication is used to instruct thetarget network device to connect to a terminal device. In theembodiments of this application, the serving access network deviceincludes a serving access network device, and the target network deviceincludes a serving access network device or a core network. When theserving access network device is a first serving access network device,and the target network device is a second RAN network element, in somefeasible embodiments, the serving access network device initiates aninterface establishment request to the target network device. Theinterface establishment request includes network slice information, andis used to exchange configurations on application sides of two connectedserving access network devices. The serving access network device sendsa target network slice service area identifier to the terminal device,where the target network slice service area identifier is used toindicate a target area, so that the terminal device determines a targetcell based on network slice configuration information and the networkslice service area identifier, where the network slice configurationinformation includes a correspondence among a network slice, an area,and a service.

With reference to the second aspect of the present invention, in a firstimplementation of the second aspect of the present invention, the methodincludes:

The serving access network device sends a handover request to the targetnetwork device, where the handover request includes the connectionindication, used to initiate handover preparation. That the servingaccess network device sends a target network slice service areaidentifier to the terminal device includes: The serving access networkdevice sends a handover command to the terminal device, where thehandover command includes the target network slice service areaidentifier, and the handover command instructs the terminal device tohandover to the target network device.

Network devices exchange network slice configuration information, sothat a network device senses slice coverage information of a neighboringcell.

With reference to the second aspect of the present invention, in asecond implementation of the second aspect of the present invention, themethod includes:

The serving access network device sends a node addition request to thetarget network device, where the node addition request includes theconnection indication. Two network devices may exchange a service areaidentifier of a network slice that is serving the terminal device orthat is required by the terminal device, where the serving accessnetwork device may trigger the target network device to perform amulti-connection operation or directly modify information about thetarget network device. That the serving access network device sends atarget network slice service area identifier to the terminal deviceincludes: The serving access network device sends a connectionreconfiguration message to the terminal device, where the connectionreconfiguration message includes the target network slice service areaidentifier, and the connection reconfiguration message is used toinstruct the terminal device to connect to the target network device.

Network devices exchange a service area identifier of a network slicethat is serving the terminal device or that the terminal device isinterested in, so that the target network device may consider theinformation to optimize mobility.

With reference to the second aspect of the present invention, in a thirdimplementation of the second aspect of the present invention, the methodincludes:

The serving access network device sends a node modification request tothe target network device, where the node modification request is usedto instruct the target network device to modify a radio resourceconfiguration of the target network device for the terminal device. Insome feasible embodiments, two network devices may exchange a servicearea identifier of a network slice that is serving the terminal deviceor that is required by the terminal device, and a primary serving accessnetwork device triggers a secondary serving access network device tomodify a current multi-connection operation. The serving access networkdevice sends a connection reconfiguration message to the terminaldevice, where the connection reconfiguration message includes the radioresource configuration.

Network devices exchange a service area identifier of a network slicethat is serving the terminal device or that the terminal device isinterested in, so that the service access network triggers the targetnetwork device to perform the multi-connection operation or modify thetarget network device.

With reference to the second aspect of the present invention, in afourth implementation of the second aspect of the present invention, themethod includes:

The serving access network device receives a node modification requestsent by the target network device. In some feasible embodiments, twonetwork devices may exchange a service area identifier of a networkslice that is serving the terminal device or that is required by theterminal device, and a secondary serving access network device initiatesmodification of a current multi-connection operation.

Network devices exchange a service area identifier of a network slicethat is serving the terminal device or that the terminal device isinterested in, so that a primary serving access network device triggersthe target network device to modify the current multi-connectionoperation.

When the terminal device that is using a target service moves, even if aserving cell changes, the terminal device can determine the target cellbased on the obtained network slice configuration information and theobtained network slice service area identifier, and continue enjoyingthe target service in the target cell, so that service continuity isensured.

A third aspect of the embodiments of the present invention provides aterminal device, including:

a first obtaining module, configured to obtain a network slice servicearea identifier from a serving access network device corresponding to aserving cell in which the terminal device is located, where the networkslice service area identifier is used to indicate an area served by anetwork slice; a determining module, configured to determine a targetcell based on network slice configuration information and the networkslice service area identifier, where the network slice configurationinformation includes a correspondence among a network slice, an area,and a service; and an access module, configured to access the targetcell.

With reference to the third aspect of the present invention, in a firstimplementation of the third aspect of the present invention, theterminal device includes:

a second obtaining module, configured to obtain the network sliceconfiguration information from a core network.

With reference to the third aspect of the present invention, in a secondimplementation of the third aspect of the present invention, theterminal device includes:

a first transmitting submodule, configured to send a request message tothe core network, where the request message is used to request thenetwork slice configuration information; and a receiving submodule,configured to receive the network slice configuration information fromthe core network.

With reference to the third aspect of the present invention, in a thirdimplementation of the third aspect of the present invention, theterminal device includes:

a second transmitting submodule, configured to send an indicationmessage to the serving access network device, where the indicationmessage is used to indicate a requirement for a network slice; and anobtaining submodule, configured to obtain the network slice service areaidentifier from the serving access network device.

A fourth aspect of the embodiments of the present invention provides aserving access network device, including:

a first transmitting module, configured to send a connection indicationto a target network device. The connection indication is used toinstruct the target network device to connect to a terminal device; anda second transmitting module, configured to send a target network sliceservice area identifier to the terminal device, where the target networkslice service area identifier is used to indicate a target area, so thatthe terminal device determines a target cell based on network sliceconfiguration information and the network slice service area identifier,where the network slice configuration information includes acorrespondence among a network slice, an area, and a service.

With reference to the fourth aspect of the present invention, in a firstimplementation of the fourth aspect of the present invention, the firsttransmitting module includes:

a first transmitting submodule, configured to send a handover request tothe target network device, where the handover request includes theconnection indication. The second transmitting module includes: a secondtransmitting submodule, configured to send a handover command to theterminal device, where the handover command includes the target networkslice service area identifier, and the handover command instructs theterminal device to handover to the target network device.

With reference to the fourth aspect of the present invention, in asecond implementation of the fourth aspect of the present invention, thefirst transmitting module includes:

a third transmitting submodule, configured to send a node additionrequest to the target network device, where the node addition requestincludes the connection indication. The second transmitting moduleincludes: a fourth transmitting submodule, configured to send aconnection reconfiguration message to the terminal device, where theconnection reconfiguration message includes the target network sliceservice area identifier, and the connection reconfiguration message isused to instruct the terminal device to connect to the target networkdevice.

With reference to the fourth aspect of the present invention, in a thirdimplementation of the fourth aspect of the present invention, theserving access network device includes:

a third transmitting module, configured to send anode modificationrequest to the target network device, where the node modificationrequest is used to instruct the target network device to modify a radioresource configuration of the target network device for the terminaldevice; and a first receiving module, configured to send a connectionreconfiguration message to the terminal device, where the connectionreconfiguration message includes the radio resource configuration.

With reference to the fourth aspect of the present invention, in afourth implementation of the fourth aspect of the present invention, theserving access network device includes:

a second receiving module, configured to receive a node modificationrequest sent by the target network device.

A fifth aspect of the embodiments of the present invention provides aterminal device, including:

a transceiver, a memory, a processor, and a bus. The transceiver, thememory, and the processor are connected by using the bus. Thetransceiver is configured to obtain a network slice service areaidentifier from a serving access network device corresponding to aserving cell in which the terminal device is located, where the networkslice service area identifier is used to indicate an area served by anetwork slice. The processor is configured to: determine a target cellbased on network slice configuration information and the network sliceservice area identifier, where the network slice configurationinformation includes a correspondence among a network slice, an area,and a service; and access the target cell. The memory is configured tostore a program, a target area, a target service, and the network sliceconfiguration information.

A sixth aspect of the embodiments of the present invention provides aserving access network device, including:

a transceiver, a memory, a processor, and a bus. The transceiver, thememory, and the processor are connected by using the bus. Thetransceiver is configured to: send a connection indication to a targetnetwork device, where the connection indication is used to instruct thetarget network device to connect to a terminal device; and send a targetnetwork slice service area identifier to the terminal device, where thetarget network slice service area identifier is used to indicate atarget area, so that the terminal device determines a target cell basedon network slice configuration information and the network slice servicearea identifier, where the network slice configuration informationincludes a correspondence among a network slice, an area, and a service.The memory is configured to store a program, a target area, a targetservice, and the network slice configuration information. The processoris configured to execute a function of the serving access networkdevice.

Another aspect of this application provides a computer readable storagemedium. The computer readable storage medium stores an instruction. Whenthe instruction is run on a computer, the computer executes the methodin the foregoing aspects.

Another aspect of this application provides a computer program productthat includes an instruction. When the instruction is run on a computer,the computer executes the method in the foregoing aspects.

It can be learned from the foregoing technical solutions that theembodiments of this application have the following advantages:

The terminal device obtains the network slice service area identifierfrom the serving access network device corresponding to the serving cellin which the terminal device is located, where the network slice servicearea identifier is used to indicate the area served by the networkslice. The terminal device determines the target cell based on thenetwork slice configuration information and the network slice servicearea identifier, where the network slice configuration informationincludes the correspondence among a network slice, an area, and aservice. The terminal device accesses the target cell. Therefore, whenthe terminal device that is using the target service moves, even if theserving cell changes, the terminal device can determine the target cellbased on the obtained network slice configuration information and theobtained network slice service area identifier, and continue enjoyingthe target service in the target cell, so that service continuity isensured.

In addition, the serving access network device sends the connectionindication to the target network device, where the connection indicationis used to instruct the target network device to connect to the terminaldevice. The serving access network device sends the target network sliceservice area identifier to the terminal device, where the target networkslice service area identifier is used to indicate the target area. Theterminal device determines the target cell based on the network sliceconfiguration information and the network slice service area identifier,where the network slice configuration information includes thecorrespondence among a network slice, an area, and a service. Therefore,when the terminal device that is using the target service moves, even ifthe serving cell changes, the terminal device can determine the targetcell based on the obtained network slice configuration information andthe obtained network slice service area identifier, and continueenjoying the target service in the target cell, so that servicecontinuity is ensured.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a framework of a network slice systemaccording to an embodiment of this application;

FIG. 2 is a schematic diagram of an embodiment of a target cell accessmethod according to an embodiment of this application;

FIG. 2.1 is a schematic diagram of an embodiment of a target cell accessmethod according to an embodiment of this application;

FIG. 3 is a schematic diagram of another embodiment of a target cellaccess method according to an embodiment of this application;

FIG. 4 is a schematic diagram of another embodiment of a target cellaccess method according to an embodiment of this application;

FIG. 5 is a schematic diagram of another embodiment of a target cellaccess method according to an embodiment of this application;

FIG. 6 is a schematic diagram of another embodiment of a target cellaccess method according to an embodiment of this application;

FIG. 7 is a schematic diagram of another embodiment of a target cellaccess method according to an embodiment of this application;

FIG. 8 is a schematic diagram of another embodiment of a target cellaccess method according to an embodiment of this application;

FIG. 9 is a schematic diagram of another embodiment of a target cellaccess method according to an embodiment of this application;

FIG. 10 is a schematic diagram of an embodiment of a terminal device1000 according to an embodiment of this application;

FIG. 1I is a schematic diagram of another embodiment of a terminaldevice 1000 according to an embodiment of this application;

FIG. 12 is a schematic diagram of another embodiment of a terminaldevice 1000 according to an embodiment of this application;

FIG. 13 is a schematic diagram of another embodiment of a terminaldevice 1000 according to an embodiment of this application;

FIG. 14 is a schematic diagram of an embodiment of a serving accessnetwork device 1400 according to an embodiment of this application;

FIG. 15 is a schematic diagram of another embodiment of a serving accessnetwork device 1400 according to an embodiment of this application;

FIG. 16 is a schematic diagram of another embodiment of a serving accessnetwork device 1400 according to an embodiment of this application;

FIG. 17 is a schematic diagram of another embodiment of a serving accessnetwork device 1400 according to an embodiment of this application;

FIG. 18 is a schematic diagram of another embodiment of a serving accessnetwork device 1400 according to an embodiment of this application;

FIG. 19 is a schematic diagram of another embodiment of a terminaldevice 1900 according to an embodiment of this application; and

FIG. 20 is a schematic diagram of another embodiment of a serving accessnetwork device 2000 according to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

The embodiments of this application provide a target cell access methodand a device, to provide a network slice service area identifier andnetwork slice configuration information for a terminal device, so thatthe terminal device accesses a target cell.

To make persons skilled in the art understand the solutions in theembodiments of this application better, the following clearly andcompletely describes the technical solutions in the embodiments of thisapplication with reference to the accompanying drawings in theembodiments of this application. Apparently, the described embodimentsare merely some but not all of the embodiments of this application.

In the specification, claims, and accompanying drawings of thisapplication, the terms “first”, “second”, “third”, “fourth”, and so on(if any) are intended to distinguish between similar objects but do notnecessarily indicate a specific order or sequence. It should beunderstood that the data termed in such a way are interchangeable inproper circumstances so that the embodiments of the present inventiondescribed herein can be implemented in other orders than the orderillustrated or described herein. Moreover, the terms “include”,“contain” and any other variants mean to cover the non-exclusiveinclusion, for example, a process, method, system, product, or devicethat includes a list of steps or units is not necessarily limited tothose expressly listed steps or units, but may include other steps orunits not expressly listed or inherent to such a process, method,system, product, or device.

As shown in FIG. 1, FIG. 1 is a schematic architectural diagram of anetwork slice system. The network slice system includes a network deviceand a terminal, and the network device includes a core network and anaccess network. A Long Term Evolution (LTE) system is used as an examplefor description in the following.

It should be noted that when a terminal device is located in a coveragearea of a cell (a carrier) provided by a macro base station or a microbase station, the terminal device communicates with the network deviceby using a transmission resource (for example, a frequency domainresource or a spectrum resource) used by the cell. The cell may be acell corresponding to the network device, and the cell may belong to amacro cell, a hyper cell, or a beam, or may belong to a base stationcorresponding to a small cell. The small cell herein may include a metrocell, a micro cell, a pico cell, a femto cell, or the like. The smallcell features a small coverage area and low transmission power, and isapplicable to providing a data transmission service of a high rate. Whenthere are a plurality of cells serving the terminal device, the terminaldevice may work in a coordinated multipoint transmission (CoMP) manner.

In an embodiment of this application, a function of the network slicesystem is implemented by using a software-defined networking (SDN)technology and a network function virtualization (NFV) technology ascore technologies.

The NFV technology implements virtualization of an underlying physicalresource, and loads a virtual network function (NF) to a generalplatform, such as a virtual machine. The SDN technology implements alogical connection between virtual machines, and constructs a pathcarrying signaling and a data flow. An end-to-end service link isconfigured by using dynamic connections between different NFs of a radioaccess network (RAN) and a core network (CN), so that a network slice isconstructed. Based on requirements of specific commercial use cases forkey performance indicator (KPI) such as a capacity, coverage, a rate, alatency, and reliability, an operator may form a specific networkfunction set and network resources required for running these networkfunctions, so that a required telecommunication service and a networkcapability service may be provided, thereby meeting a specific marketscenario and requirement.

It should be noted that in the 3GPP, a current discussion related to anetwork architecture is mainly focused on network slice selection. Thenetwork slice selection aims to select an appropriate network slice foruser equipment (UE), and associate the terminal device with a specificnetwork slice, so as to establish a corresponding control plane (CP)and/or a user plane (UP) connection to the network slice.

In some feasible embodiments, when the terminal device needs to beassociated with a network slice or handover a network slice, anappropriate network slice may be selected for and associated with theterminal device based on network slice guiding, that is, a correspondingnetwork slice identifier (NSID) is allocated to the terminal device.Specifically, the NSID is selected for the terminal device in twonetwork slice guiding manners, so as to implement a complete procedureof the network slice selection.

Guiding manner 1: A network slice identifier (NSID) is pre-configured ina universal subscriber identity module (USIM) card of the terminaldevice. Guiding manner 2: In a process in which the terminal deviceregisters with a public land mobile network (PLMN), a network allocatesan NSID to the terminal device.

The two manners are respectively corresponding to different scenarios.After the network slice guiding ends, the terminal device stores oneNSID for each PLMN, and uses the NSID in the following process ofcommunication with the PLMN, and the NSID is used by the network toassociate the terminal device with a corresponding network slice.

This application is used to resolve a problem of how a serving accessnetwork device considers deployment of a network slice and mobility of aterminal device. That is, for a network slice restricted by a servicearea, the mobility of the terminal device is considered. When theterminal device moves, service continuity of the network slice for theterminal device is improved. Specifically, a terminal device in an idlestate learns of information about a coverage area of a required networkslice, so that the terminal device can increase a priority for selectingor reselecting cells covered by the required network slice, to accessthese cells as much as possible. In addition, when the terminal devicehas accessed the network slice, and moves to a coverage edge of acurrent cell, and handover needs to be performed between a source celland a target cell, a source serving access network device needs toselect an appropriate target serving access network device, to ensurethat the target serving access network device can provide a service ofthe network slice accessed by the terminal device or re-select anothernetwork slice and ensure that a handover procedure is successfullyperformed.

In some feasible embodiments, this application is also applicable to aUniversal Mobile Telecommunications System (UMTS) system, a CDMA system,a wireless local area network (WLAN), or a future 5G (the fifthgeneration) wireless communications system, such as a new radio (NR)system or evolved LTE (eLTE) of a new radio access technology. That is,an access network device in the eLTE may simultaneously connect to acore network of the LTE, a core network of the future 5G, and the like.

In the embodiments of this application, the network device may be adevice that is in an access network and that communicates with andconnects to a terminal over an air interface by using a sector. Thenetwork device may be configured to mutually convert a receivedover-the-air frame and an Internet Protocol (IP) packet, and act as arouter between the terminal device and a remaining part of the accessnetwork. The remaining part of the access network may include an IPnetwork. The network device may further coordinate attribute managementof the air interface. For example, the network device may be a basetransceiver station (BTS) in a Global System for Mobile communications(GSM) or a Code Division Multiple Access (CDMA) technology; or may be aNodeB in Wideband Code Division Multiple Access (WCDMA); or may be anevolved NodeB (eNB, or e-NodeB, evolutional Node B) in the LTE. This isnot limited herein.

In the embodiments of this application, a RAN device may be an accesspoint (AP) in the WLAN or a base transceiver station (BTS) in the GSM orCDMA; or may be a NodeB (NB) in the WCDMA; or may be an evolved NodeB(Evolutional Node B, eNB or eNodeB) in the LTE, a relay station or anaccess point, an in-vehicle device, a wearable device, a network devicein a future 5G network, or a network device in a future evolved PLMNnetwork, for example, a base station, a transmission and reception point(TRP), a centralized unit (CU), or a distributed unit (DU) that canconnect to a 5G core network device. A CN device may be a mobilitymanagement entity (MME) or a gateway in the LTE, or may be a controlplane (CP) network function (NF) or a user plane (UP) network functionin the 5G network, for example, a common control plane network function(CCNF) or a session management network function (SMF). The servingaccess network device may be a server, may greatly vary due to differentconfigurations or different performance, and may include one or morecentral processing units (CPU) (for example, one or more processors) anda memory, and one or more storage media (for example, one or more massstorage devices) for storing application programs or data. The memoryand the storage medium may be transient storage or persistent storage. Aprogram stored in the storage medium may include one or more modules(not shown in the figure), and each module may include a series ofinstruction operations for a server. Further, the central processingunit may be configured to communicate with the storage medium, toperform, on the server, a series of instruction operations in thestorage medium.

The server may further include one or more power supplies, one or morewired or wireless network interfaces, one or more input/outputinterfaces, and/or one or more operating systems such as WindowsServer™, Mac OS X™, Unix™, Linux™, or FreeBSD™.

Particularly, it should be noted that the terminal device mentioned inthe embodiments of this application may be a device that provides a userwith voice and/or data connectivity, a handheld device with a radioconnection function, or another processing device connected to awireless modem. A wireless terminal may communicate with a core networkthrough a radio access network (RAN). The wireless terminal may be amobile terminal, such as a mobile phone (or referred to as a “cellular”phone) and a computer with a mobile terminal, for example, may be aportable, pocket-sized, handheld, computer built-in, or in-vehiclemobile apparatus, which exchanges voice and/or data with the radioaccess network. For example, the wireless terminal may be a device suchas a personal communication service (PCS) phone, a cordless telephoneset, a Session Initiation Protocol (SIP) phone, a wireless local loop(WLL) station, or a personal digital assistant (PDA). The wirelessterminal may also be referred to as a system, a subscriber unit ( ), asubscriber station, a mobile station, a mobile station, a remotestation, an access point, a remote terminal, an access terminal), a userterminal, a terminal device, a user agent, a user device, or userequipment.

A mobile phone is used as an example, and a structure of the mobilephone may include components such as a radio frequency (RF) circuit, amemory, an input unit, a display unit, a sensor, an audio frequencycircuit, a Wireless Fidelity (WiFi) module, a processor, and a powersupply. Persons skilled in the art may understand that, the structure ofthe mobile phone shown in FIG. 11 does not constitute a limitation onthe mobile phone, and the mobile phone may include more or fewercomponents than those shown in the figure, or combine some components,or have different component arrangements.

In the embodiments of this application, the terminal device obtains anetwork slice service area identifier from a serving access networkdevice corresponding to a serving cell in which the terminal device islocated, where the network slice service area identifier is used toindicate an area served by a network slice. The terminal devicedetermines a target cell based on network slice configurationinformation and the network slice service area identifier, where thenetwork slice configuration information includes a correspondence amonga network slice, an area, and a service. The terminal device accessesthe target cell. Therefore, when the terminal device that is using atarget service moves, even if the serving cell changes, the terminaldevice can determine the target cell based on the obtained network sliceconfiguration information and the obtained network slice service areaidentifier, and continue enjoying the target service in the target cell,so that service continuity is ensured.

In addition, the serving access network device sends a connectionindication to a target network device, where the connection indicationis used to instruct the target network device to connect to the terminaldevice. The serving access network device sends a target network sliceservice area identifier to the terminal device, where the target networkslice service area identifier is used to indicate a target area, so thatthe terminal device determines the target network device based on thetarget area, the target service, and the pre-obtained network sliceconfiguration information, and accesses a target cell served by a targetnetwork. Therefore, when the terminal device that is using the targetservice moves, even if the serving cell changes, the terminal device candetermine the target cell based on the obtained network sliceconfiguration information and the obtained network slice service areaidentifier, and continue enjoying the target service in the target cell,so that service continuity is ensured.

For ease of understanding, the following describes a specific procedurein the embodiments of this application. The terminal device obtainsnetwork slice information in different manners, and the manners areseparately described in the following.

I. The Terminal Device Separately Obtains Related Information from aCore Network and a Serving Access Network Device.

Referring to FIG. 2, an embodiment of a target cell access method in anembodiment of this application includes the following steps.

201. The terminal device obtains a network slice service area identifierfrom a serving access network device corresponding to a serving cell inwhich the terminal device is located, where the network slice servicearea identifier is used to indicate an area served by a network slice.

In some feasible embodiments, the serving access network device mayfurther send network slice service area identification information tothe terminal device. It should be noted that the network slice servicearea identifier stored by the serving access network device may bepreconfigured by a network management system such as an operation,administration, and maintenance (OAM) entity, or may be preconfigured byan application layer function entity. This is not limited herein. Itshould be noted that the terminal device may obtain one or more networkslice service area identifiers. This is not limited herein.

Further, in some feasible embodiments, the network slice service areaidentification information may be a system message sent by using a radioresource control (RRC) message, and the system message may be includedin an existing system message block as a newly-added field, or may beused as a new system message block and sent to the terminal device. Thisis not limited herein. The network slice service area identificationinformation may alternatively be a dedicated message for the terminaldevice sent by using an RRC message, and only the terminal device cancorrectly receive and decode the message, so that another terminaldevice cannot receive the message in this case.

Further, in some feasible embodiments, at least one network sliceidentifier included in the network slice service area identificationinformation may be sorted based on a priority, that is, a network sliceservice area priority. The network slice service area priority is usedto indicate a priority corresponding to the network slice service areaidentifier, for example, a priority of a network slice service area A ishigher than that of a network slice service area B.

Further, in some feasible embodiments, the network slice service areaidentifier may indicate a coverage area of a network slice, and thenetwork slice may cover a group of cells in one PLMN. Each cell maybelong to one or more network slice service areas. The network sliceservice area identifier may further indicate that the network slicecovers all cells in the entire PLMN.

Further, the network slice service area identifier may be a specificpredefined value, or may be a group of cell identifiers, a group ofserving access network device identifiers, or a tracking area (TA) TAidentifier list.

Further, in some feasible embodiments, after receiving the network sliceservice area identifier, the terminal device may determine a coveragearea of a network slice corresponding to the identifier, and maydetermine a service or a service type that may be provided by thenetwork slice.

Further, in some feasible embodiments, the network slice service areaidentification information includes but is not limited to the followingrelated information: information about a frequency channel number ofeach frequency in a same frequency list or different frequency listsupported by a cell; and a network slice service area identifiersupported by the frequency channel number, where the network sliceservice area identifier is used to uniquely identify a network sliceservice area, and the area may be a sector, a beam, a cell, a trackingarea, a paging area, a serving access network device station, atransmission and reception point (TRP), a distributed unit (DU), acentralized unit (CU), or the like. This is not limited herein.

In some feasible embodiments, information about a frequency channelnumber of each frequency in a same frequency list or different frequencylist supported by a neighboring cell and a network slice service areaidentifier supported by the frequency channel number are used touniquely identify a network slice service area. The area may be asector, a beam, a cell, a tracking area, a paging area, a serving accessnetwork device station, a TRP, a DU, a CU, or the like. This is notlimited herein.

It should be noted that there may be many divided cells of a servingaccess network device. For example, a base station has many antennas,and each antenna may form a sector-shaped cell. A cell that the terminaldevice accesses and information about the cell are included herein.

202. The terminal device determines a target cell based on network sliceconfiguration information and the network slice service area identifier,where the network slice configuration information includes acorrespondence among a network slice, an area, and a service.

In some feasible embodiments, the terminal device may use the receivednetwork slice configuration information and the received network sliceservice area identification information as a standard for cell selectionand reselection. Further, for a terminal device that is being served bythe service, the service type, and/or the network slice, the terminaldevice may set, to a highest priority, an identifier of a currentcamping cell that can provide the service and/or a frequency and afrequency channel number of the current camping cell. When performingcell reselection, the terminal device may preferentially reselect a cellcorresponding to the cell identifier, and/or a cell corresponding to thefrequency and the frequency channel number.

Further, for a terminal device that needs to be served by the service,the service type, and/or the network slice, when the terminal deviceexpects to be served by the service, the service type, and/or thenetwork slice, the terminal device may set, to a highest priority, anidentifier of a current camping cell that can improve the service and/ora frequency and a frequency channel number of the current camping cell.When performing cell reselection, the terminal device may preferentiallyreselect a cell corresponding to the frequency and the cell identifier,and/or a cell corresponding to the frequency channel number.

Further, when there is no service, service type, and/or network slicerequired by the terminal device, for example, a session ends, theterminal device no longer sets, to the highest priority, the frequencyand the frequency channel number of the current camping cell that canimprove the service.

203. The terminal device accesses the target cell.

204. The terminal device obtains the network slice configurationinformation from the core network.

Optionally, referring to FIG. 2.1, this embodiment may further includestep 204, and step 204 is performed before step 201.

In this embodiment of this application, an identifier of a tracking area(TA) may be pre-allocated to each cell, for example, a TA identifier ofa cell 1 is TA1. Different network slices have different service ranges.For example, a network slice 1 needs to cover TA1, TA2, and TA3, anetwork slice 2 needs to cover TA2, TA4, and TA5, and a network slice 3covers only TA6. This is not limited herein.

In this embodiment of this application, the terminal device may receivenetwork slice configuration information sent by the core network or afunction entity related to an application layer or a service layer,where the network slice configuration information includes acorrespondence between a network slice and a service. Specifically, forexample, the network slice configuration information indicates that thenetwork slice 1 can provide a service 1, a service 2, and a service 3,and the network slice 2 can provide a service 3, a service 4, and aservice 5.

Optionally, in some feasible embodiments, the network sliceconfiguration information may be preconfigured in device storage of theterminal device or a storage unit of a subscriber identity module (SIM)card, or the configuration message may be sent to the terminal device byusing a non-access stratum (NAS) message, and the terminal device storesthe received network slice configuration information.

Further, in some feasible embodiments, the network slice configurationinformation may further include but is not limited to the followingrelated information: a service, for example, a video, a sports program,or a television channel, or a service type corresponding to one or moreservices, for example, an identifier corresponding to a video typeservice, such as a temporary mobile group identity (TMGI), used toindicate the service, the channel, or the service type; a time at whicha session corresponding to a service or a service type starts and/orends, used to indicate a time at which the service starts or ends;frequency information corresponding to a service or a service type, usedto indicate a frequency or a frequency channel number only or at leastat which the service or the service type can provide a service; anetwork slice service area identifier corresponding to a service or aservice type, where the service may be corresponding to one or morenetwork slice service area identifiers, and the service may be enjoyedonly in cells corresponding to the network slice service areaidentifiers; network slice identification information corresponding to aservice or a service type; and a network slice identifier that isallocated to a network slice and indicated by network sliceidentification information.

The network slice identification information corresponding to a serviceor a service type may include but is not limited to: a network slicetype, such as information indicating a network slice type, for example,enhanced mobile broadband (eMBB), ultra-reliable and low latencycommunications (URLLC), or massive machine type communications (mMTC),where the network slice type may further be an end-to-end network slicetype, including a RAN and the CN, or may be a network slice type of theserving access network device, or a network slice type of the corenetwork; a service type, related to a specific service, such asinformation indicating a service feature or a specific service, forexample, a video service, an Internet of Vehicles service, or a voiceservice; tenant information, used to indicate information about acustomer establishing or leasing a network slice, for example, Tencentor State Grid; terminal device group information, used to indicateinformation about a group into which a user is grouped based on afeature such as a level of the user; slice group information, used toindicate an instance identifier that the terminal device may accessbased on a feature, or used to indicate an instance identifier andfeature information, for example, an identifier is allocated to anetwork slice instance and is used to indicate the network sliceinstance, or a new identifier is mapped based on a network sliceinstance identifier, the identifier is associated with the network sliceinstance, and a receiver may identify a represented specific networkslice instance based on the identifier; and a dedicated core network(DCN) identifier, where the identifier is used to uniquely indicate adedicated core network, for example, a dedicated core network of theInternet of Things, and optionally, there may be a mapping relationshipbetween a DCN identifier and a network slice identifier, the networkslice identifier may be obtained based on the mapped DCN identifier, andthe DCN identifier may be obtained based on the mapped network sliceidentifier. In some feasible embodiments, the network sliceconfiguration information may further include other requiredinformation. This is not limited herein.

It should be noted that after receiving the network slice configurationinformation, the terminal device may store the network sliceconfiguration information, and synchronize with a connected servingaccess network device, for example, perform detection on a primarysynchronization signal and a secondary synchronization signal, andperform correction in time domain and frequency domain, so as to obtaininformation such as a corresponding frequency channel number andbandwidth. In other words, the terminal device synchronizes with theserving access network device in both time domain and frequency domain.For example, when a base station needs to send information, the terminaldevice needs to obtain a precise moment at which the information issent. In some feasible embodiments, the terminal device needs tosynchronize with the RAN before the terminal device initiatescommunication with the RAN.

II. The Terminal Device Obtains Related Information from a Core Network.

301. The terminal device sends a request message to the core network,where the request message is used to request network slice configurationinformation.

In some feasible embodiments, the terminal device may establish anetwork connection to a serving access network device, for example, anRRC connection. After the network connection is established, theterminal device may perform uplink and downlink data communication withthe serving access network device, and perform, by using the servingaccess network device, uplink and downlink data communication with acore network that serves the serving access network device.

Optionally, in some feasible embodiments, the terminal device sends therequest message to the core network. In some feasible embodiments, themessage may be a NAS message, for example: an attach request, used torequest the terminal device to attach to or register with the CN; aservice request, used to request the terminal device to establish aservice with the CN; a session establishment request, used to requestthe terminal device to establish a session with the CN; or a trackingarea update request, used to request the terminal device and the CN toupdate a tracking area when the terminal device moves out of a currenttracking area.

In some feasible embodiments, the request message may be an RRC message,for example: an RRC connection setup request, used to request toestablish an RRC connection to a network element of the serving accessnetwork device; an RRC connection re-establishment request, used torequest to re-establish an RRC connection to a network element of theserving access network device; RRC connection setup complete, used toindicate that a process of establishing an RRC connection to a networkelement of the serving access network device is complete; or capabilityinformation transmission of the terminal device, used to notify theserving access network device of capability information of the terminaldevice. This is not limited herein.

Further, the request message may include but is not limited to thefollowing information: a temporary identifier of the terminal device,allocated to the terminal device by the core network, and used touniquely indicate the terminal device connected to the network element;a serving access network device identifier, used to identify the servingaccess network device in a globally unique manner; a cell identifier,used to identify the cell in a globally unique manner; a network sliceidentifier; or a network slice service area identification informationrequest, used to request the core network to deliver a network sliceservice area identifier supported by the serving access network deviceand/or the cell. In some feasible embodiments, the request message isnot limited to the foregoing messages, and is not limited herein.

302. The terminal device receives the network slice configurationinformation from the core network.

In some feasible embodiments, the core network may reply to the terminaldevice with a message, and the message includes network sliceinformation. Further, the message may be a NAS message, for example:attach permission, used to indicate that the CN grants the attachrequest of the terminal device; service request permission, used toindicate that the CN grants the service request of the terminal device;or session establishment, used to indicate that the CN establishes asession for the terminal device.

Further, the message includes but is not limited to the followinginformation: a serving access network device identifier, used toidentify the serving access network device in a globally unique manner;or network slice service area identification information supported by aserving cell and a neighboring cell, such as network slice service areaidentification information supported in a list of all frequencies orfrequency channel numbers supported by the serving cell and theneighboring cell. In some feasible embodiments, the message may furtherinclude other required information. This is not limited herein. Theterminal device may store the received network slice information, andthe network slice information includes the network slice service areaidentification information.

303. The terminal device determines a target cell based on the networkslice configuration information and a network slice service areaidentifier, where the network slice configuration information includes acorrespondence among a network slice, an area, and a service.

304. The terminal device accesses the target cell.

In this embodiment, step 303 and step 304 are the same as step 203 andstep 204 in the foregoing embodiment, and details are not describedherein.

III. The Terminal Device Obtains Related Information from a ServingAccess Network Device.

401. The terminal device sends an indication message to the servingaccess network device, where the indication message is used to indicatea requirement for a network slice.

In this embodiment of this aspect, the terminal device may notify theserving access network device of network slice requirement information,so that the serving access network device senses the requirement of theterminal device for the network slice, so as to improve mobility.

In this embodiment of this application, the terminal device may firstsynchronize with the serving access network device, for example, performdetection on a primary synchronization signal and a secondarysynchronization signal, and perform correction in time domain andfrequency domain, so as to obtain information such as a correspondingfrequency channel number and bandwidth.

Then, the terminal device sends the indication message to the servingaccess network device, to indicate information about the requirement ofthe terminal device for the network slice. Further, the message may besent by using a random access resource, such as a specific random accesspreamble or a specific random access time-frequency resource. Themessage may alternatively be a MAC control element message, and themessage may be an RRC message, for example: an RRC connection setuprequest, used to request to establish an RRC connection to a networkelement of the serving access network device; an RRC connectionre-establishment request, used to request to re-establish an RRCconnection to a network element of the serving access network device;RRC connection setup complete, used to indicate that a process ofestablishing an RRC connection to a network element of the servingaccess network device is complete; or capability informationtransmission of the terminal device, used to notify the serving accessnetwork device of capability information of the terminal device. This isnot limited herein.

Further, the indication message may include but is not limited to thefollowing messages: a service area identifier of a network slice that isserving the terminal device; information about a frequency or frequencychannel number corresponding to the service area identifier of thenetwork slice that is serving the terminal device; a service areaidentifier of a network slice required by the terminal device;information about a frequency or frequency channel number correspondingto the service area identifier of the network slice required by theterminal device; and a network slice service area priority, used toindicate a priority corresponding to a network slice service areaidentifier, for example, a priority of a network slice A is higher thanthat of a network slice B.

In this embodiment of this application, the serving access networkdevice may store the indication information. Optionally, a networkelement on an access network side may obtain, for handover preparation,information about a requirement capability of the terminal device forthe network slice. This is not limited herein.

402. The terminal device obtains a network slice service area identifierfrom a serving access network device corresponding to a serving cell inwhich the terminal device is located, where the network slice servicearea identifier is used to indicate an area served by a network slice.

403. The terminal device determines a target cell based on network sliceconfiguration information and the network slice service area identifier,where the network slice configuration information includes acorrespondence among a network slice, an area, and a service.

404. The terminal device accesses the target cell.

In this embodiment, step 402 to step 404 are the same as step 202 tostep 204 in the foregoing embodiment, and details are not describedherein.

The foregoing separately describes different embodiments of a method forobtaining network slice information by a terminal device in theembodiments of the present invention, and the following describes anetwork slice information exchange between network devices in theembodiments of the present invention. Network devices exchange networkslice information in different manners, and the manners are separatelydescribed in the following.

I. A Serving Access Network Device Sends Network Slice Information to aTarget Network Device.

In the embodiments of this application, two serving access networkdevices may exchange the network slice information, so that a firstserving access network device learns of slice coverage information of asecond serving access network device. Referring to FIG. 5, anotherembodiment of a target cell access method in an embodiment of thisapplication includes the following steps.

501. The serving access network device sends a connection indication tothe target network device, where the connection indication is used toinstruct the target network device to connect to a terminal device.

In this embodiment of this application, the serving access networkdevice includes a serving access network device, and the target networkdevice includes a serving access network device or a core network. Whenthe serving access network device is the first serving access networkdevice, and the target network device is a second RAN network element,in some feasible embodiments, the serving access network deviceinitiates an interface establishment request to the target networkdevice. The interface establishment request includes network sliceinformation, and is used to exchange configurations on application sidesof two connected serving access network devices. Further, the messageincludes but is not limited to the following information: a servingaccess network device identifier, used to identify the serving accessnetwork device in a globally unique manner; information about a servingcell and a neighboring cell of each serving cell, for example, cellidentifiers, physical cell identifiers, information about frequencychannel numbers, tracking area codes, and supported network sliceservice area identification information respectively corresponding tothe serving cell and the neighboring cell of each serving cell; or anetwork slice service area priority, used to indicate a prioritycorresponding to a network slice service area identifier, for example, apriority of a network slice service area A is higher than that of anetwork slice service area B.

502. The target network device may send an interface establishmentrequest response to the serving access network device, to exchangeconfigurations on application sides of two connected serving accessnetwork devices.

Further, the message includes but is not limited to the followinginformation: a serving access network device identifier, used toidentify the serving access network device in a globally unique manner;information about a serving cell and a neighboring cell of each servingcell, for example, cell identifiers, physical cell identifiers,information about frequency channel numbers, tracking area codes, andsupported network slice service area identification informationrespectively corresponding to the serving cell and the neighboring cellof each serving cell; or a network slice service area priority, used toindicate a priority corresponding to a network slice service areaidentifier, for example, a priority of a network slice service area A ishigher than that of a network slice service area B.

503. The serving access network device initiates an interfaceconfiguration update to the target network device, to transmit updatedinformation.

Further, the message includes but is not limited to the followinginformation, a serving access network device identifier, used toidentify the serving access network device in a globally unique manner;change information of information about a serving cell and a neighboringcell of each serving cell, used to perform an operation such as adding anew cell, modifying an existing cell configuration, or deleting a cell,for example, cell identifiers, physical cell identifiers, informationabout frequency channel numbers, tracking area codes, and supportednetwork slice service area identification information respectivelycorresponding to the serving cell and the neighboring cell of eachserving cell, or a network slice service area priority, used to indicatea priority corresponding to a network slice service area identifier, forexample, a priority of a network slice service area A is higher thanthat of a network slice service area B.

504. The target network device initiates an interface configurationupdate acknowledgement message to the serving access network device, toacknowledge that a configuration update message of the serving accessnetwork device is received.

Optionally, if the target network device cannot support interfaceconfiguration update content initiated by the serving access networkdevice, the target network device may reply with a failure message, toindicate that a configuration update of the serving access networkdevice fails.

After obtaining the network slice information, the terminal devicedetermines a target network slice based on a target area, a targetservice, and the network slice information, and the target network sliceis used to carry the target service in the target area. When theterminal device is located in the target area and uses the targetservice, the terminal device is associated with the target networkslice.

II. A Serving Access Network Device Sends a Handover Request to a TargetNetwork Device.

In an embodiment of this application, in a handover process, the servingaccess network device and the target network device may exchange aservice area identifier of a network slice that is serving a terminaldevice or that is required by a terminal device. A target serving accessnetwork device may consider the information to optimize mobility. Forexample, in a handover preparation phase, a target RAN devicepreferentially uses, as a new target RAN device after handover, anetwork device corresponding to the service area identifier of thenetwork slice that is serving the terminal device or that is required bythe terminal device. Referring to FIG. 6, another embodiment of a targetcell access method in an embodiment of this application includes thefollowing steps.

601. The serving access network device sends a handover request to thetarget network device. The handover request includes a connectionindication.

The serving access network device may send the handover request to thetarget network device, to initiate handover preparation. Further, themessage includes but is not limited to the following information:

service area identification information of a network slice that isserving the terminal device:

service area identification information of a network slice required bythe terminal device;

a network slice service area priority, used to indicate a prioritycorresponding to a network slice service area identifier, for example, apriority of a network slice service area A is higher than that of anetwork slice service area B:

a cause for handover, used to indicate a cause for handover this time,for example, a cause on a radio network layer (such as handovertriggered caused by a signal or resource optimization);

a target cell identifier, used to uniquely indicate an identifier of atarget cell; a handover restriction list, including a serving PLMN, anequivalent PLMN, a list of forbidden or allowed tracking areas, a listof forbidden or allowed cells, or the like:

a temporary identifier corresponding to the terminal device, used by acore network to search for a stored context of the terminal device;

an identifier of a core network control function entity associated withthe terminal device;

a network slice identifier corresponding to one or more or all networkslices selected by the terminal device:

information of a bearer that needs to be established and that iscorresponding to one or more or all network slices selected by theterminal device, for example, a bearer identifier, a bearer level QoS(quality of service) parameter, an endpoint of a tunnel, or bearer levelsecurity information, for example, a ciphering function enabling option,where a location of a ciphering function is in the serving accessnetwork device and/or the core network, a header compression functionenabling option, where a location of a header compression function is inthe serving access network device and/or the core network, or anintegrity protection enabling option, where a location of integrityprotection is in the serving access network device and/or the corenetwork:

session information that needs to be established and that iscorresponding to one or more or all network slices selected by theterminal device, for example, a session identifier, a session level QoS(quality of service) parameter, an endpoint of a tunnel, or a sessionlevel security information, for example, a ciphering function enablingoption, where a ciphering function is located in the serving accessnetwork device and/or the core network, a header compression functionenabling option, where a location of a header compression function is inthe serving access network device and/or the core network, or anintegrity protection enabling option, where a location of integrityprotection is in the serving access network device and/or the corenetwork:

information of flow that needs to be established and that iscorresponding to one or more or all network slices selected by theterminal device, for example, a flow identifier, a flow level QoSparameter, an endpoint of a tunnel, or flow level security information,for example, a ciphering function enabling option, where a location of aciphering function is in the serving access network device and/or thecore network, a header compression function enabling option, where alocation of a header compression function is in the serving accessnetwork device and/or the core network, or an integrity protectionenabling option, where a location of integrity protection is in theserving access network device and/or the core network; or

context information of the terminal device, for example, a network sliceidentifier corresponding to one or more or all network slices subscribedby the terminal device which is not limited herein.

602. The target network device replies to the serving access networkdevice with handover request acknowledgement, to indicate that thetarget network device has prepared resources.

Further, the message includes but is not limited to the followinginformation:

an old serving access network device identifier;

a new serving access network device identifier;

a transparent container (container) from a target node to a source node,including an RRC handover command;

a network slice service area identifier, a list of a bearer, a session,and/or a flow that are/is not admitted, and the network slice servicearea identifier, the bearer, session, and/or flow are/is correspondingto one or more or all network slices selected by the terminal device; or

information of a bearer, a session, and/or a flow that is admitted, andthe bearer, session, and/or flow are/is corresponding to the one or moreor all network slices selected by the terminal device, for example, abearer identifier, a session identifier, a flow identifier, a bearerlevel QoS parameter, or an endpoint of a tunnel which is not limitedherein.

603. The serving access network device sends a handover command to theterminal device. The handover command includes a target network sliceservice area identifier. The handover command instructs the terminaldevice to handover to the target network device.

The serving access network device may initiate an RRC message to theterminal device, to carry the handover command. Further, the messageincludes but is not limited to the following information: network sliceservice area identification information supported by the target cell;the target cell identifier; a new temporary identifier of the terminaldevice; or a bearer configuration, for example, configuration on a PDCP,a Radio Link Control (RLC) protocol, Media Access Control (MAC), and aphysical layer.

The terminal device establishes an RRC connection to the target networkdevice, and initiates a handover complete message such as RRC connectionreconfiguration complete to the target network device, to indicate thathandover is complete.

Optionally, in some feasible embodiments, when a process of handoverusing an interface between a RAN device and a CN device needs to betriggered, for example, when there is no direct terrestrial sideinterface or no wireless backhaul link between the serving accessnetwork device and the target network device, the serving access networkdevice may further initiate a handover request to the CN device. Forspecific message content, refer to the handover request message in step601, where the message is used to initiate handover preparation. The CNdevice forwards the received message to the target network device, andthe target network device replies to the CN device with handover requestacknowledgement, to indicate that the target network device has preparedthe resources. For specific message content, refer to the handoverrequest acknowledgement message in step 602. Then, the CN deviceforwards the received message to the serving access network device.

II. A Serving Access Network Device Sends a Node Addition Request to aTarget Network Device.

In an embodiment of this application, two network devices may exchange aservice area identifier of a network slice that is serving a terminaldevice or that is required by a terminal device, where the servingaccess network device may trigger the target network device to perform amulti-connection operation or directly modify information about thetarget network device. Referring to FIG. 7, another embodiment of atarget cell access method in an embodiment of this application includesthe following steps.

701. The serving access network device sends a node addition request tothe target network device. The node addition request includes aconnection indication.

The serving access network device may send the node addition request tothe target network device, to request the target network device toestablish a multi-connection operation, so as to allocate a radioresource for the terminal device. Further, the message includes but isnot limited to the following information:

identification information of a network slice that is serving theterminal device;

identification information of a network slice that the terminal deviceis allowed to access:

service area identification information of the network slice that isserving the terminal device;

service area identification information of a network slice required bythe terminal device;

a network slice service area priority, used to indicate a prioritycorresponding to a network slice service area identifier, for example, apriority of a network slice service area A is higher than that of anetwork slice service area B;

configuration information of a network slice corresponding to a networkslice identifier, for example, a physical random access channel (PRACH)configuration, a random access preamble configuration, a configurationrelated to security, or a configuration related to radio resourcemanagement, which is not limited herein; a security capability of theterminal device, used to indicate a ciphering algorithm and an integrityprotection algorithm that are supported by the terminal device:

a security key of the target network device, used by the target networkdevice to perform data encryption for the terminal device;

an aggregate maximum bit rate of the terminal device applicable to thetarget network device, including an uplink aggregate maximum bit rateand a downlink aggregate maximum bit rate;

a serving PLMN, used to indicate a PLMN corresponding to a radio bearerthat needs to be established by the target network device:

information of a bearer that needs to be established and thatcorresponds to one or more or all network slices selected by theterminal device, session information, and/or flow information, forexample, a bearer type, such as, a master cell group bearer, a secondarycell group bearer, or a split bearer, a bearer identifier, informationabout quality of service corresponding to a bearer, an endpoint of atunnel, a session identifier, a flow identifier, information aboutquality of service corresponding to a session, information about qualityof service corresponding to a flow, information about security of bearerlevel, session level, or flow level, for example, a ciphering functionenabling option, where a location of a ciphering function is in theserving access network device and/or a core network, a headercompression function enabling option, where a location of a headercompression function is in the serving access network device and/or acore network, or an integrity protection enabling option, where alocation of integrity protection is in the serving access network deviceand/or a core network; or

a handover restriction list, including a serving PLMN, an equivalentPLMN, a list of forbidden or allowed tracking areas, a list of forbiddenor allowed cells, or the like which are not limited herein.

702. The target network device replies a serving access network deviceaddition request acknowledgement to the serving access network device,to indicate that the target network device has prepared resources.

Further, the message includes but is not limited to the followinginformation: a list of a bearer, a session, and/or a flow that is notadmitted, and the bearer, session and/or flow are/is corresponding toone or more or all network slices selected by the terminal device;information of a bearer, a session, and/or a flow that is admitted, andthe bearer, session and/or flow that are/is corresponding to the one ormore or all network slices selected by the terminal device, for example,a bearer identifier, a session identifier, a flow identifier, bearerlevel QoS parameter, or an endpoint of a tunnel; or a transparentcontainer from a target node to a source node, including bearerconfiguration information generated by the target network device.

Further, if the target network device cannot support any receivednetwork slice, radio bearer, session, flow, or the like, or an erroroccurs during a process, the target network device replies with arejection message carrying a cause, for example, the network slice, theradio bearer, the session, the flow, or the like cannot be supported.

703. The serving access network device sends a connectionreconfiguration message to the terminal device. The connectionreconfiguration message includes a target network slice service areaidentifier. The connection reconfiguration message is used to instructthe terminal device to connect to the target network device.

In some feasible embodiments, the serving access network device mayinitiate an RRC connection reconfiguration message to the terminaldevice. The RRC connection reconfiguration message carries radioresource configuration information, used to instruct the terminal deviceto perform radio resource configuration based on the received message.Further, the message includes but is not limited to the followinginformation: a network slice service area identifier supported by thetarget network device; a target cell identifier; a new temporaryidentifier of the terminal device; or a bearer configuration, forexample, configurations on a PDCP. RLC. MAC, and a physical layer.

704. The terminal device replies to the serving access network devicewith RRC connection reconfiguration complete, to indicate that theterminal device completes radio resource configuration.

705. The serving access network device sends serving access networkdevice configuration complete to the target network device, to indicatethat the terminal device has completed the radio resource configuration.

IV. A Serving Access Network Device Sends a Serving Access NetworkDevice Modification Request to a Target Network Device.

801. The serving access network device sends a node modification requestto the target network device, where the node modification request isused to instruct the target network device to modify a radio resourceconfiguration of the target network device for a terminal device.

In some feasible embodiments, two network devices may exchange a servicearea identifier of a network slice that is serving the terminal deviceor that is required by the terminal device, and a primary serving accessnetwork device triggers a secondary serving access network device tomodify a current multi-connection operation. Specifically, the servingaccess network device initiates the serving access network devicemodification request to the target network device, to request the targetnetwork device to modify current context information of the terminaldevice and radio resource allocation prepared by the target networkdevice for the terminal device. Further, the message includes but is notlimited to the following information:

identification information of a network slice that is serving theterminal device; identification information of a network slice that theterminal device is allowed to access;

service area identification information of the network slice that isserving the terminal device:

service area identification information of a network slice required bythe terminal device;

a network slice service area priority, used to indicate a prioritycorresponding to a network slice service area identifier, for example, apriority of a network slice service area A is higher than that of anetwork slice service area B;

a secondary cell group bearer modification indication, used to indicatewhether a secondary cell group bearer needs to be modified;

a security capability of the terminal device, used to indicate aciphering algorithm and an integrity protection algorithm that aresupported by the terminal device:

a security key of the target network device, used by the target networkdevice to perform data ciphering on the terminal device:

an aggregate maximum bit rate of the terminal device applicable to thetarget network device, including an uplink aggregate maximum bit rateand a downlink aggregate maximum bit rate:

information of a bearer that needs to be established, modified, orreleased and that is corresponding to one or more or all network slicesselected by the terminal device, session information, and/or flowinformation, for example, a bearer type, such as, a master cell groupbearer, a secondary cell group bearer, a split bearer, a beareridentifier, information about quality of service corresponding to abearer, an endpoint of a tunnel, a session identifier, a flowidentifier, information about quality of service corresponding to asession, information about quality of service corresponding to a flow,information about security of a bearer level, session level, or flowlevel, for example, a ciphering function enabling option, where alocation of a ciphering function is in the serving access network deviceand/or a core network, a header compression function enabling option,where a location of a header compression function is in the servingaccess network device and/or a core network, or an integrity protectionenabling option, where a location of integrity protection is in theserving access network device and/or a core network; or

a handover restriction list, including a serving PLMN, an equivalentPLMN, a list of forbidden or allowed tracking areas, a list of forbiddenor allowed cells, or the like. This is not limited herein.

802. The target network device replies to the serving access networkdevice with serving access network device modification requestacknowledgement, to acknowledge the modification request of the targetnetwork device.

Further, the message includes but is not limited to the followinginformation: a list of a bearer, a session, and/or a flow that is notadmitted, and the bearer, session, and/or flow are/is corresponding toone or more or all network slices selected by the terminal device;information of a bearer, a session, and/or a flow that is admitted, andthe bearer, session, and/or flow are/is corresponding to the one or moreor all network slices selected by the terminal device, for example,admitted bearer information, admitted session information, and/oradmitted flow information that need/needs to be added, modified, orreleased, a bearer identifier, a session identifier, a flow identifier,a bearer level QoS parameter, or an endpoint of a tunnel; or atransparent container from a target node to a source node, includingbearer configuration information generated by the target network device.Further, if the target network device cannot support any receivednetwork slice, radio bearer, session, flow, or the like, or an erroroccurs in a process, the target network device replies with a rejectionmessage carrying a cause, for example, the network slice, the radiobearer, the session, the flow, or the like cannot be supported. This isnot limited herein.

803. The serving access network device sends a connectionreconfiguration message to the terminal device, where the connectionreconfiguration message includes the radio resource configuration.

Further, the message includes but is not limited to the followinginformation: a network slice service area identifier supported by thetarget network device; a target cell identifier a new temporaryidentifier of the terminal device; or a bearer configuration, forexample, configurations on a PDCP, RLC, MAC, and a physical layer.

804. The terminal device replies to the serving access network devicewith connection reconfiguration complete, to indicate that the terminaldevice completes radio resource configuration.

805. The serving access network device sends serving access networkdevice configuration complete to the target network device, to indicatethat the terminal device completes the radio resource configuration.

V. A Serving Access Network Device Receives a Node Modification RequestMessage Sent by a Target Network Device.

901. The serving access network device receives a node modificationrequest sent by the target network device.

In some feasible embodiments, two network devices may exchange a servicearea identifier of a network slice that is serving a terminal device orthat is required by a terminal device, and a secondary serving accessnetwork device initiates modification of a current multi-connectionoperation. Specifically, the serving access network device may initiatethe node modification request to the target network device, to triggerto release a radio resource, modify a primary serving cell, invert aPacket Data Convergence Protocol (PDCP) sequence number, or the like.

Further, the message includes but is not limited to the followinginformation:

identification information of a network slice that is serving theterminal device;

identification information of a network slice that the terminal deviceis allowed to access;

service area identification information of the network slice that isserving the terminal device;

service area identification information of a network slice required bythe terminal device;

a network slice service area priority, used to indicate a prioritycorresponding to a network slice service area identifier, for example, apriority of a network slice service area A is higher than that of anetwork slice service area B;

a secondary cell group bearer modification indication, used to indicatewhether a secondary cell group bearer needs to be modified:

information of a bearer that needs to be released and that iscorresponding to one or more or all network slices selected by theterminal device, session information, and/or flow information, forexample, a bearer type, such as, a master cell group bearer, a secondarycell group bearer, a split bearer, a bearer identifier, informationabout quality of service corresponding to a bearer, an endpoint of atunnel, a session identifier, a flow identifier, information aboutquality of service corresponding to a session, information about qualityof service corresponding to a flow, information about security of abearer level, session level, or flow level, for example, a cipheringfunction enabling option, where a location of a ciphering function is inthe serving access network device and/or a core network, a headercompression function enabling option, where a location of a headercompression function is in the serving access network device and/or acore network, or an integrity protection enabling option, where alocation of integrity protection is in the serving access network deviceand/or a core network; or

a handover restriction list, including a serving PLMN, an equivalentPLMN, a list of forbidden or allowed tracking areas, a list of forbiddenor allowed cells, or the like.

902. The serving access network device initiates a serving accessnetwork device modification request to the target network device.

Optionally, when a data forwarding address, a security key of asecondary RAN device, or the like needs to be provided, the servingaccess network device initiates a RAN device modification request to thetarget network device, to request the target network device to modifycurrent context information of the terminal device and radio resourceallocation prepared by the target network device for the terminaldevice. Further, the message includes but is not limited to:

identification information of a network slice that is serving theterminal device;

identification information of a network slice that the terminal deviceis allowed to access;

service area identification information of the network slice that isserving the terminal device:

service area identification information of a network slice required bythe terminal device;

a network slice service area priority, used to indicate a prioritycorresponding to a network slice service area identifier, for example, apriority of a network slice service area A is higher than that of anetwork slice service area B:

a secondary cell group bearer modification indication, used to indicatewhether a secondary cell group bearer needs to be modified:

a security capability of the terminal device, used to indicate aciphering algorithm and an integrity protection algorithm that aresupported by the terminal device;

a security key of the target network device, used by the target networkdevice to perform data ciphering on the terminal device;

an aggregate maximum bit rate of the terminal device applicable to thetarget network device, including an uplink aggregate maximum bit rateand a downlink aggregate maximum bit rate:

information of a bearer that needs to be established, modified, orreleased and that is corresponding to one or more or all network slicesselected by the terminal device, session information, and/or flowinformation, for example, a bearer type, such as, a master cell groupbearer, a secondary cell group bearer, a split bearer, a beareridentifier, information about quality of service corresponding to abearer, an endpoint of a tunnel, a session identifier a flow identifier,information about quality of service corresponding to a session,information about quality of service corresponding to a flow,information about security of a bearer level, a session level, or a flowlevel, for example, a ciphering function enabling option, where alocation of a ciphering is in a RAN device and/or a CN device, a headercompression function enabling option, where a location of a headercompression function is in a RAN device and/or a CN device, or anintegrity protection enabling option, where a location of integrityprotection is in a RAN device and/or a CN device; or

a handover restriction list, including a serving PLMN, an equivalentPLMN, a list of forbidden or allowed tracking areas, a list of forbiddenor allowed cells, or the like.

903. The target network device replies to the serving access networkdevice with node modification request acknowledgement, to indicate thatthe target network device has prepared resources.

Further, the message includes but is not limited to the followinginformation: a list of a bearer, a session, and/or a flow that is notadmitted, and the bearer, session, and/or flow are/is corresponding toone or more or all network slices selected by the terminal device;information of a bearer, session, and/or flow that is admitted, and thebearer, session, and/or flow is corresponding to the one or more or allnetwork slices selected by the terminal device, for example, admittedbearer information, admitted session information, and/or admitted flowinformation that need/needs to be added, modified, or released, a beareridentifier, a session identifier, a flow identifier, a bearer level QoSparameter, or an endpoint of a tunnel, or a transparent container from atarget node to a source node, including bearer configuration informationgenerated by the target network device.

Further, if the target network device cannot support any receivednetwork slice, radio bearer, session, flow, or the like, or an erroroccurs in a process, the target network device replies with a rejectionmessage carrying a cause, for example, the network slice, the radiobearer, the session, the flow, or the like cannot be supported.

904. The target network device replies to the serving access networkdevice with serving access network device modification requestacknowledgement, to acknowledge the modification request of the targetnetwork device.

Further, the message includes but is not limited to the followinginformation: a list of a bearer, a session, and/or a flow that is notadmitted, and the bearer, session, and/or flow are/is corresponding toone or more or all network slices selected by the terminal device;information of a bearer, session information, and/or flow that isadmitted, and the bearer, session, and/or flow are/is corresponding tothe one or more or all network slices selected by the terminal device,for example, admitted bearer information, admitted session information,and/or admitted flow information that need/needs to be added, modified,or released, a bearer identifier, a session identifier, a flowidentifier, a bearer level QoS parameter, or an endpoint of a tunnel; ora transparent container from a target node to a source node, includingbearer configuration information generated by the target network device.

Further, if the target network device cannot support any receivednetwork slice, radio bearer, session, flow, or the like, or an erroroccurs in a process, the target network device replies with a rejectionmessage carrying a cause, for example, the network slice, the radiobearer, the session, the flow, or the like cannot be supported.

905. The serving access network device initiates an RRC connectionreconfiguration message to a terminal device, where the RRC connectionreconfiguration message carries radio resource configurationinformation, to instruct the terminal device to perform radio resourceconfiguration based on the received message.

Further, the message includes but is not limited to the followinginformation: a network slice service area identifier supported by thetarget network device; a target cell identifier; a new temporaryidentifier of the terminal device; or a bearer configuration, forexample, configurations on a PDCP, RLC, MAC, and a physical layer. Thisis not limited herein.

906. The terminal device replies to the serving access network devicewith RRC connection reconfiguration complete, to indicate that theterminal device completes radio resource configuration.

907. The serving access network device sends serving access networkdevice configuration complete to the target network device, to indicatethat the terminal device completes the radio resource configuration.

The foregoing describes the target cell access method, and the followingdescribes a related device. Referring to FIG. 10, FIG. 10 shows aterminal device 1000, including

a first obtaining module 1001, configured to obtain a network sliceservice area identifier from a serving access network devicecorresponding to a serving cell in which the terminal device is located,where the network slice service area identifier is used to indicate anarea served by a network slice:

a determining module 1002, configured to determine a target cell basedon network slice configuration information and the network slice servicearea identifier, where the network slice configuration informationincludes a correspondence among a network slice, an area, and a service,and

an access module 1003, configured to access the target cell.

Referring to FIG. 11, the terminal device 1000 further includes:

a second obtaining module 1004, configured to obtain the network sliceconfiguration information from a core network.

Referring to FIG. 12, the second obtaining module 1004 includes:

a first transmitting submodule 10041, configured to send a requestmessage to the core network, where the request message is used torequest the network slice configuration information; and

a receiving submodule 10042, configured to receive the network sliceconfiguration information from the core network.

Referring to FIG. 13, the first obtaining module 1001 includes:

a second transmitting submodule 10011, configured to send an indicationmessage to the serving access network device, where the indicationmessage is used to indicate a requirement for a network slice; and

an obtaining submodule 10012, configured to obtain the network sliceservice area identifier from the serving access network device.

Referring to FIG. 14, FIG. 14 shows a serving access network device1400, including:

a first transmitting module 1401, configured to send a connectionindication to a target network device. The connection indication is usedto instruct the target network device to connect to a terminal device;and

a second transmitting module 1402, configured to send a target networkslice service area identifier to the terminal device, where the targetnetwork slice service area identifier is used to indicate a target area,so that the terminal device determines a target cell based on networkslice configuration information and the network slice service areaidentifier, where the network slice configuration information includes acorrespondence among a network slice, an area, and a service.

Referring to FIG. 15, the first transmitting module 1401 includes:

a first transmitting submodule 14011, configured to send a handoverrequest to the target network device. The handover request includes theconnection indication.

The second transmitting module 1402 includes:

a second transmitting submodule 14021, configured to send a handovercommand to the terminal device, where the handover command includes thetarget network slice service area identifier, and the handover commandinstructs the terminal device to handover to the target network device.

Referring to FIG. 16, the first transmitting module 1401 includes:

a third transmitting submodule 14012, configured to send a node additionrequest to the target network device, where the node addition requestincludes the connection indication.

The second transmitting module 1402 includes:

a fourth transmitting submodule 14022, configured to send a connectionreconfiguration message to the terminal device, where the connectionreconfiguration message includes the target network slice service areaidentifier, and the connection reconfiguration message is used toinstruct the terminal device to connect to the target network device.

Referring to FIG. 17, the serving access network device 1400 furtherincludes:

a third transmitting module 1403, configured to send anode modificationrequest to the target network device, where the node modificationrequest is used to instruct the target network device to modify a radioresource configuration of the target network device for the terminaldevice; and

a first receiving module 1404, configured to send a connectionreconfiguration message to the terminal device, where the connectionreconfiguration message includes the radio resource configuration.

Referring to FIG. 18, the serving access network device 1400 furtherincludes:

a second receiving module 1405, configured to receive a nodemodification request sent by the target network device.

The foregoing describes the embodiments of this application from aperspective of a modular function entity, and the following describesthe embodiments of this application from a perspective of hardwareprocessing. Referring to FIG. 19, an embodiment of this applicationprovides a terminal device 1900, including:

a transceiver 1901, a memory 1902, a processor 1903, and a bus 1904.

The transceiver 1901, the memory 1902, and the processor 1903 areconnected by using the bus 1904.

The transceiver 1901 is configured to obtain a network slice servicearea identifier from a serving access network device corresponding to aserving cell in which the terminal device is located, where the networkslice service area identifier is used to indicate an area served by anetwork slice.

The transceiver 1901 may include a communications interface between theprocessor 1903 and a standard communications subsystem.

The transceiver 1901 may further include a communications interface inan EIA-RS-232C standard, namely, a communications interface in a serialbinary data exchange interface technology standard between data terminalequipment (DTE) and data circuit-terminating equipment (DCE), or mayinclude a communications interface in an RS-485 protocol. This is notlimited herein.

The processor 1903 is configured to: determine a target cell based onnetwork slice configuration information and the network slice servicearea identifier, where the network slice configuration informationincludes a correspondence among a network slice, an area, and a service;and access the target cell.

The processor 1903 may be a central processing unit (CPU), a networkprocessor (NP), or a combination of a CPU and an NP.

The processor 1903 may further include a hardware chip. The hardwarechip may be an application-specific integrated circuit (ASIC), aprogrammable logic device (PLD), or a combination thereof. The PLD maybe a complex programmable logical device (CPLD), a field-programmablegate array (FPGA), generic array logic (GAL), or any combinationthereof.

The memory 1902 is configured to store a program, a target area, atarget service, and the network slice configuration information.

The memory 1902 may include a volatile memory, for example, a randomaccess memory (RAM). The memory 402 may also include a nonvolatilememory, for example, a flash memory, a hard disk (HDD), or a solid statedrive (SSD). The memory 403 may further include a combination of theforegoing memories. This is not limited herein.

Optionally, the memory 1902 may be further configured to store a programinstruction. The processor 403 may invoke the program instruction storedin the memory 1902, to perform the step or the optional implementationin the embodiment shown in FIG. 2, so that the terminal device 1900implements the function in the foregoing method.

Referring to FIG. 20, FIG. 20 shows a serving access network device2000, including:

a transceiver 2001, a memory 2002, a processor 2003, and a bus 2004.

The transceiver 2001, the memory 2002, and the processor are connectedby using the bus.

The transceiver 2001 is configured to: send a connection indication to atarget network device, where the connection indication is used toinstruct the target network device to connect to a terminal device; andsend a target network slice service area identifier to the terminaldevice, where the target network slice service area identifier is usedto indicate a target area, so that the terminal device determines atarget cell based on network slice configuration information and thenetwork slice service area identifier, where the network sliceconfiguration information includes a correspondence among a networkslice, an area, and a service.

The transceiver 2001 may include a communications interface between theprocessor 2003 and a standard communications subsystem.

The transceiver 2001 may further include a communications interface inan EIA-RS-232C standard, namely, a communications interface in a serialbinary data exchange interface technology standard between data terminalequipment (DTE) and data circuit-terminating equipment (DCE), or mayinclude a communications interface in an RS-485 protocol. This is notlimited herein.

The memory 2002 is configured to store a program, a target area, atarget service, and the network slice configuration information.

The memory 2002 may include a volatile memory, for example, a randomaccess memory (RAM). The memory 402 may also include a nonvolatilememory, for example, a flash memory, a hard disk drive (HDD), or a solidstate drive (SSD). The memory 403 may further include a combination ofthe foregoing memories. This is not limited herein.

Optionally, the memory 2002 may be further configured to store a programinstruction. The processor 403 may invoke the program instruction storedin the memory 2002, to perform the step or the optional implementationin the embodiment shown in FIG. 2, so that the serving access networkdevice 2000 implements the function in the foregoing method.

The processor 2003 is configured to execute a function of the servingaccess network device.

The processor 2003 may be a central processing unit (CPU), a networkprocessor (NP), or a combination of a CPU and an NP.

The processor 2003 may further include a hardware chip. The hardwarechip may be an application-specific integrated circuit (ASIC), aprogrammable logic device (PLD), or a combination thereof. The PLD maybe a complex programmable logical device (CPLD), a field-programmablegate array (FPGA), generic array logic (GAL), or any combinationthereof.

It may be clearly understood by persons skilled in the art that, for thepurpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, reference may bemade to a corresponding process in the foregoing method embodiments, anddetails are not described herein.

In the several embodiments provided in this application, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiment is merely an example. For example, the unit division ismerely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected according toactual needs to achieve the objectives of the solutions of theembodiments.

All or some of the foregoing embodiments may be implemented by usingsoftware, hardware, firmware, or any combination thereof. When softwareis used to implement the embodiments, the embodiments may be implementedcompletely or partially in a form of a computer program product.

The computer program product includes one or more computer instructions.When the computer program instructions are loaded and executed on thecomputer, the procedures or functions according to the embodiments ofthe present invention are all or partially generated. The computer maybe a general-purpose computer, a dedicated computer, a computer network,or another programmable apparatus. The computer instructions may bestored in a computer-readable storage medium or may be transmitted froma computer-readable storage medium to another computer-readable storagemedium. For example, the computer instructions may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, a coaxial cable, anoptical fiber, or a digital subscriber line (DSL)) or wireless (forexample, infrared, radio, or microwave) manner. The computer-readablestorage medium may be any usable medium accessible by a computer, or adata storage device, such as a server or a data center, integrating oneor more usable media. The usable medium may be a magnetic medium (forexample, a floppy disk, a hard disk, or a magnetic tape), an opticalmedium (for example, a DVD), a semiconductor medium (for example, asolid state disk Solid State Disk, (SSD)), or the like.

In conclusion, the foregoing embodiments are merely intended fordescribing the technical solutions of this application, but not forlimiting this application. Although this application is described indetail with reference to the foregoing embodiments, persons of ordinaryskill in the art should understand that they may still makemodifications to the technical solutions described in the foregoingembodiments or make equivalent replacements to some technical featuresthereof, without departing from the scope of the technical solutions ofthe embodiments of this application.

1. A handover method, comprising: sending, by a serving access networkdevice to a target access network device, a handover request to initiatehandover preparation, wherein the handover request comprises anidentifier of a session, and a session level security information, andwherein the session level security information comprises a cipheringfunction enabling option indicating whether a ciphering function isenabled for the session and an integrity protection enabling optionindicating whether integrity protection is enabled for the session;receiving, by the serving access network device from the target accessnetwork device, a handover request acknowledgement; and sending, by theserving access network device, a handover command to a terminal device.2. The method according to claim 1, wherein the handover request furthercomprises a network slice identifier, and the network slice identifiercomprises a network slice type.
 3. The method according to claim 1,wherein network slice type comprises at least one of enhanced mobilebroadband, ultra-reliable and low latency communications, or massivemachine type communications.
 4. The method according to claim 1, whereinthe handover request further comprises a flow identifier and a flowlevel quality of service (QoS) parameter.
 5. The method according toclaim 1, wherein handover request acknowledgement comprises a list of anadmitted session.
 6. The method according to claim 5 wherein thehandover request acknowledgement further comprises a list of a flow thatis not admitted.
 7. A communications system for handover, comprising: aserving access network device; and a target access network device,wherein the serving access network device comprises at least oneprocessor, the at least one processor is coupled to a memory storingprogramming instructions executable by the at least one processor toperform operations comprising: sending a handover request to the targetaccess network device to initiate handover preparation, wherein thehandover request comprises an identifier of a session, and a sessionlevel security information, and wherein the session level securityinformation comprises a ciphering function enabling option indicatingwhether a ciphering function is enabled for the session and an integrityprotection enabling option indicating whether integrity protection isenabled for the session; and sending a handover command to a terminaldevice; and wherein the target access network device comprises at leastone processor, the at least one processor is coupled to a memory storingprogramming instructions executable by the at least one processor toperform operations comprising sending a handover request acknowledgementto the serving access network device.
 8. The communications system ofclaim 7, wherein the handover request further comprises a network sliceidentifier, and the network slice identifier comprises a network slicetype.
 9. The communications system of claim 8, wherein network slicetype comprises at least one of enhanced mobile broadband, ultra-reliableand low latency communications, or massive machine type communications.10. The communications system of claim 7, wherein the handover requestfurther comprises a flow identifier and a flow level quality of service(QoS) parameter.
 11. The communications system of claim 7, whereinhandover request acknowledgement comprises a list of an admittedsession.
 12. The communications system of claim 11, wherein handoverrequest acknowledgement further comprises a list of a flow that is notadmitted.
 13. A communications apparatus, comprising: at least oneprocessor, the at least one processor is coupled to a memory storingprogramming instructions executable by the at least one processor toperform operations comprising: sending a handover request to a targetaccess network device to initiate handover preparation, wherein thehandover request comprises an identifier of a session, and a sessionlevel security information, and wherein the session level securityinformation comprises a ciphering function enabling option indicatingwhether a ciphering function is enabled for the session and an integrityprotection enabling option indicating whether integrity protection isenabled for the session; receiving a handover request acknowledgementfrom the target access network device; and sending a handover command toa terminal device.
 14. The communications apparatus according to claim13, wherein the handover request further comprises a network sliceidentifier, and the network slice identifier comprises a network slicetype.
 15. The communications apparatus according to claim 13, whereinnetwork slice type comprises: at least one of enhanced mobile broadband,ultra-reliable and low latency communications, or massive machine typecommunications.
 16. The communications apparatus according to claim 13,wherein the handover request further comprises a flow identifier and aflow level quality of service (QoS) parameter.
 17. The communicationsapparatus according to claim 13, wherein handover requestacknowledgement comprises a list of an admitted session.
 18. Thecommunications apparatus according to claim 17, wherein handover requestacknowledgement further comprises a list of a flow that is not admitted.